static variable inside a function

[jhapk]

Hi,

is there any reason for declaring a local variable inside a function as static?

thanks

[Disch]

A static variable has a global lifetime but with local scope. This lets you have the benefits of having a singular global and the organizational benefit of keeping the scope local.

void CountIt()
{
  static int count = 0;

  ++count;
  cout << count << "\n";
}

int main()
{
  CountIt();  // prints 1
  CountIt();  // prints 2
  CountIt();  // prints 3, etc
}

[Galik]

Yes, the static variable will retain its value between calls.

[buffbill]

Nope.......a static variable is referred to once and once only.

[Disch]

?

What do you mean "referred to"?

It's initialized only once (barring some unfortunate multithreaded race condition) -- but it can be accessed as many times as the program likes.

[helios]

It's initialized only once (barring some unfortunate multithreaded race condition)

Static and global data is initialized before main() is called, one object at a time. There's no room for race conditions because it's all ran from a single thread.

[Disch]

local static variables are initialized on first use. If the function is called at the same time from 2 threads, you could have a race condition.

edit:

illustration:

#include <iostream>

using namespace std;

class A
{
public:
    A()
    {
        cout << "A ctor\n";
    }
};

void func()
{
    static A a;
}

int main()
{
    cout << "main starting\n";
    func();
    return 0;
}